Enhanced Innate Immunity Mediated by IL-36α in Atopic Dermatitis and Differences in Cytokine Profiles of Lymphocytes in the Skin and Draining Lymph Nodes.

(1) Background: The IL-36 cytokines have been identified as key contributors to pustular psoriasis, and their inhibitor is already in clinical use. However, few studies have explored them in atopic dermatitis. (2) Methods: The role of IL-36α was investigated in various atopic dermatitis models using wild-type, keratin 14-specific IL-33 transgenic, IL-18 transgenic, caspase-1 transgenic, and caspase-1 transgenic mice with IL-17AF deletion, reflecting diverse aspects of human skin inflammation. IL-36α was administered subcutaneously in five doses on alternate days across the five strains to examine cellular infiltration patterns and cytokine expression levels. (3) Results: The skin phenotype was exacerbated, accompanied by worsening edema and skin thickness in all mouse groups upon IL-36α administration. An increase in infiltrating cells was observed among innate immune cells, while lymphocyte counts, including T cells and innate lymphoid cells, did not rise. Additionally, anti-inflammatory cytokines were induced simultaneously with inflammatory cytokines and downstream cytokines of IL-36α as well. Infiltrating lymphocytes in the skin displayed a distinct Type 2 cytokine-dominant profile for innate lymphoid cells and a Type 3 cytokine-dominant profile for T helper cells and γδ T cells, contrasting with the Type 1-dominant cell profile in draining lymph nodes. Type 1, Type 2, and Type 3 cytokine dominance patterns were not affected by the administration of IL-36α. (4) Conclusions: IL-36α triggers inflammatory responses in atopic dermatitis by activating innate immunity. The infiltrating lymphocytes in the skin have different cytokine production profiles between innate lymphoid cells and T cells, as well as different patterns of cytokine production in their draining lymph nodes.